Topical ophthalmic solutions, or eye drops, are currently the most commonly used method of ocular drug delivery. Eye drops account for approximately 90% of all ophthalmic medications, but are very inefficient. Eye drops are administered by pulse delivery, which is characterized by a transient overdose, followed by a relatively short period of effective therapeutic concentration, and then a prolonged period of insufficient concentration or under-dosing. Furthermore, each drop is diluted and washed away by reflex tearing and blinking so that only 1 to 7% of an eye drop is absorbed by the eye. The remainder is either flushed onto the patient's cheek or drained through the nasolacrimal system.
Ophthalmic ointments, which are viscous semisolid preparations, may be the most commonly used alternative to liquid eye drops. Due to their greater viscosity, ointments have a longer contact time with the cornea and possibly provide more opportunity for drug absorption than a solution. The viscous nature of ointments, however, distorts and blurs the patient's vision. Injections into the vitreous, subconjunctival space, and sub Tenon's space are also alternative methods of drug delivery for some medications. Due to the associated discomfort, risk of infection, and lack of patient enthusiasm for ocular injections, however, drug delivery by injection is typically reserved for drugs which have poor water solubility or cannot be adequately delivered by topical means. There remains a need to increase the availability of medications to the eye, to increase the exposure time of the medication to the eye, and to more effectively deliver to the eye drugs that cannot be applied effectively and efficiently as topical drops.
The concept of delivering a medication to the eye through a contact lens was introduced as early as 1960. While the uptake and release of medications from conventional soft contact lenses has been explored, there remains a need to provide a contact lens device that can deliver drug to the eye in a controlled, sustained release manner. Furthermore, it would be desirable to provide a contact lens drug delivery device that is relatively simple in design, that does not require complicated and expensive manufacturing processes, that does not significantly impair or interfere with the patient's vision, and that would not require a substantial change in the practice patterns of eye physicians and surgeons. It would also be desirable for the drug delivery device in use to be substantially unnoticeable to the casual observer of the patient.